H.F.
I agree that maybe she should have more of a varied diet but a little pot belly is totally normal at this age. Kids really don't start losing their baby fat or their little buddha bellies until they're 3. It's really so easy to feed kids fresh and healthy so here's some ideas:
Breakfast: Oatmeal (great idea!) mixed with applesauce. Homemade pancakes/waffles that you can freeze. The beauty of homemade is is that you can add healthy things like banana, pumpkin, or whole wheat to the mix.
snacks: Diced banana, graham crackers, cereal bars, cheese, and yogurt. I mostly buy Greek yogurt because it's super high in protein. Trader Joes is an excellent place to get snacks! Most of it is organic, low sugar, and it's usually cheaper than the grocery brands. My son loves their cereal bars and they're half the price of the Nutri grain ones. Homemade (healthy) muffins. My son loves banana bran muffins that I keep in the freezer and just take out for a snack. For snacks I try to offer fruit and healthy carbs.
Lunch: Quesadillas (I do refried beans and cheese and then cut into little bits for self feeding), pasta with diced bits of veggies (mine loves broccoli), diced tofu, diced chicken. I tried to stay away from frozen and processed foods for the most part. A lot times, I serve our leftover dinners from the night before for lunch and he loves it.
Dinner: He eats what we eat:) I just take out the meat or whatever else we're having and dice it small for him. I think the biggest mistake we make is thinking that kids won't eat what we eat...big mistake! He'll eat curry, stir fry, salmon, pasta, chicken and just about anything. I try to avoid fruit at dinner and sometimes lunch because then he just wants that. Sometimes if he's having an off night or what we're having is too spicy I give him a veggie burger. I just heat it up and dice it up into small pieces for him.
I know it's hard being a single mom who works full time (been there!) but with a little planning you can feed her really healthy! Take a little time on the weekend to cook and freeze a few things, that's a huge time saver for me.
Good luck and I hope this helps. ~H.